Steering control apparatus

Abstract

A steering control apparatus of the present invention comprises a steering state detector for detecting a steering state of a steering system; a return determining device for detecting a change of the steering state on the steering system by detecting the steering state and thereafter detecting the change of the steering state thus detected, based on the steering state detected by the steering state detector; and a torque imparting device for imparting a torque for returning the steering system to the neutral position, to the steering system when the return determining device detects the change of the steering state. The steering control apparatus of the present invention is able to improve the accuracy of a return decision of the steering system and to suitably impart a return assist torque for returning the steering system to the neutral position.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a steering control apparatus for imparting a return torque for returning a steering system to its neutral position. [0003] 2. Related Background of the Invention [0004] In automobiles, as friction of a steering system increases or as tire returnability becomes weaker, the friction of the steering system and the tire return force balance each other out up to a larger steer angle, so as to degrade steering wheel returnability. Particularly, where the steering system is equipped with an electric power steering system, the steering wheel returnability becomes more degraded because of friction between gears for transmitting a torque generated by a motor, inertia of the motor, and so on. In order to enhance the steering wheel returnability, some electric power steering systems are configured to impart a return torque for returning the steering wheel to the neutral position when the driver ...

AI Technical Summary

Benefits of technology

[0005] However, the conventional return decision method sometimes suffered degradation of decision accuracy, which can result in imparting the return torque when not required, or which can fail to impart the return torque when necessary. If the return torque is imparted when not required, the driver must give a steering torque against the return torque. If the return torque is not imparted when needed, it will result in degrading the returnability and worsening driver's steering feeling. In case that the steering angular velocity and the steering torque both are small at small steering angles, it is very difficult to whether the direction of steering torque is different from that of steering angular velocity or not. And in case that the steering torque suddenly decreases at the time of driver's releasing the steering wheel after having turned it, it is also very difficult to determine whether the direction of steering torque is different from that of steering angular velocity or not. An object of the present invention is therefore to provide a steering control apparatus capable of improving the accuracy of the return decision of the steering system.

[0008] In the steering control apparatus, when the return determining means detects a change of the steering state (i.e., when it detects a return to the neutral position from the steered state of the steering system), the torque imparting means imparts the torque for returning the steering system (e.g., a steering wheel or steered road-wheels), to improve the returnability of the steering system. In this manner, the steering control apparatus is able to highly accurately detect a return of the steering system from the steered state to the neutral position and to securely impart the torque for assisting the return during the return operation of the steering system to the neutral position. As a result, the return torque is imparted to the steering system only when necessary, so as to improve the steering feeling.

[0016] The above steering control apparatus of the present invention may have a configuration wherein when the torque imparting means continuously imparts the torque for not less than a predetermined time, the operation of imparting the torque for returning the steering system to the neutral position is terminated. In this steering control apparatus, since it is assumed that there is some anomaly if the steering system is not back in the neutral state even after the torque for returning the steering system to the neutral position is continuously imparted, it is determined that there is an abnormality if the torque is continuously imparted for not less than the predetermined time, and the operation of imparting the torque is terminated. This fail-safe mechanism prevents an unnecessary torque from being continuously imparted to the steering system.

Problems solved by technology

However, the conventional return decision method sometimes suffered degradation of decision accuracy, which can result in imparting the return torque when not required, or which can fail to impart the return torque when necessary.

If the return torque is not imparted when needed, it will result in degrading the returnability and worsening driver's steering feeling.

In case that the steering angular velocity and the steering torque both are small at small steering angles, it is very difficult to whether the direction of steering torque is different from that of steering angular velocity or not.

And in case that the steering torque suddenly decreases at the time of driver's releasing the steering wheel after having turned it, it is also very difficult to determine whether the direction of steering torque is different from that of steering angular velocity or not.

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